1. Field of the Invention
The present invention relates in general to an energy harvesting system/method and, more particularly, to a method/system that includes a thermostrictive material and a piezoelectric element, such as, a laminate capable of harvesting waste heat.
2. Description of Related Art
Waste heat is always generated whenever work is done. Harvesting such waste heat can increase the efficiency of engines, be used to power numerous devices (eliminating the need for auxiliary power sources), and in general, significantly reduce power requirements. Various methods have been used to try and harvest such waste heat, the most important of which is through thermoelectric materials.
In order to efficiently convert waste heat to usable electrical energy, thermoelectric materials generally requires a large Seebeck coefficient having a “figure of merit” or Z, defined as Z=S2/ρK, where S is the Seebeck coefficient, ρ is the electrical resistivity, and K is the thermal conductivity. The Seebeck coefficient is further defined as the ratio of the open-circuit voltage to the temperature difference between the hot and cold junctions of a circuit exhibiting the Seebeck effect, or S=V/(Th31 Tc). Therefore, in searching for a good thermoelectric material, materials with large values of S, and low values of ρ and K are beneficial.
However, current state of the art thermoelectric materials utilized to harvest waste heat and convert such heat to a useful energy, for example, devices that use a combination of n-type and p-type materials, generally have Seebeck coefficients on the order of several 100 μV°K−1, which is too low for practical applications.
Background information for thermoelectric devices is described and claimed in U.S. Pat. No. 5,550,387, entitled “Superlattice Quantum Well Material,” issued Aug. 27, 1996 to Elsner et al., including the following, “The present invention provides thermoelectric elements having a very large number of alternating layers of semiconductor material, the alternating layers all having the same crystalline structure. This makes the vapor deposition process easy because the exact ratio of the materials in the layers is not critical. The inventors have demonstrated that materials produced in accordance with this invention provide figures of merit more than six times that of prior art thermoelectric materials. A preferred embodiment is a superlattice of Si, as a barrier material, and SiGe, as a conducting material, both of which have the same cubic structure. Another preferred embodiment is a superlattice of B—C alloys, the layers of which would be different stoichiometric forms of B—C but in all cases the crystalline structure would be alpha rhombohedral. In a preferred embodiment the layers are grown under conditions as to cause them to be strained at their operating temperature range in order to improve the thermoelectric properties.”
Background information on an energy harvesting system is described and claimed in U.S. Pat. No. 2004/0238022 A1, entitled “Thermoelectric Power From Environmental Temperature Cycles,” issued Dec. 2, 2004 to Hiller et al., including the following, “The present invention provides an electric generator system for producing electric power from the environmental temperature changes such as occur during a normal summer day on Earth or Mars. In a preferred embodiment a phase-change mass is provided which partially or completely freezes during the relatively cold part of a cycle and partially or completely melts during the relatively hot part of the cycle. A thermoelectric module is positioned between the phase-change mass and the environment. The temperature of the phase-change mass remains relatively constant throughout the cycle. During the hot part of the cycle heat flows from the environment through the thermoelectric module into the phase change mass generating electric power which is stored in an electric power storage device such as a capacitor or battery. During the cold part of the cycle heat flows from the phase change mass back through the module and out to the environment also generating electric power that also is similarly stored. An electric circuit is provided with appropriate diodes to switch the direction of the current between the hot and cold parts of the cycle. A preferred phase change mass is a solution of water and ammonia that has freeze points between about 270 K to about 145 K depending on the water ammonia ratio. Preferably, a finned unit is provided to efficiently transfer heat from a module surface to the environment.”
A need exists for an improved thermoelectric method and system configured as, for example, a laminate so as to harvest waste heat as energy. The present invention is directed to such a need.